(1) Field of the Invention
The present invention relates to an apparatus and a method for analysis of particulate material in fluid, especially, to the apparatus and the method for analysis of the particulate material, which are preferable for measurement of particle size of the particulate material existing in pure liquid such as ultra pure water used in a manufacturing process of semiconductor or in production of pure gas.
(2) Description of the Prior Art
As a method for measurement of particle size of ultra fine particles, which is the particulate material, a laser breakdown method which utilizes plasma formation by irradiates a particle with an intense laser pulse is effective. As for such methods, prior art are disclosed in JP-A-62-38345 (1987) and JP-A-1-116433 (1989). In JP-A-62-38345 (1987), the number of particles is counted by detecting sonic waves which are generated by a laser breakdown which is caused only when the particle is existing in a sensitive region where energy is larger than the laser breakdown threshold value) by collecting pulsed laser beam, and setting energy density of the laser beam higher than the laser breakdown threshold value of the particle and lower than the laser breakdown threshold value of the medium Further, the particle size is measured by using a tendency that generated intensity of the sonic wave is proportional to the particle size
On the other hand, in JP-A-1-116433 (1989), the particle size is measured by detecting only intensity of emission line spectrum of elements which is included in generated plasma emission at the breakdown.
The prior art described above has a problem that precision of the particle size measurement is not necessarily high because of neglecting the fluctuation in intensity of the sonic wave and intensity of the plasma emission which are caused by difference of absorbed quantity of light by plasma depending on the position (the position of the particle in the sensitive portion) where the breakdown occurred Especially, the prior art has a problem that ultra fine particle having a particle diameter less than 0.1 .mu.m is not detectable with preferable reproducibility.
Further, as the prior art disclosed in JP-A-1-116433 (1989) uses bright line spectrum which is only a part of plasma emission, sensitivity is not necessarily high, and detection of ultrafine particle having a particle diameter of 0.1 .mu.m at largest was impossible.